1. Field of the Disclosure
The disclosure relates to a differential gear including a final drive mechanism and a differential gear mechanism, and particularly, to a differential gear that can restrain a failure occurrence at the time of lubrication of a rolling bearing included in a final drive mechanism.
2. Description of Related Art
As a differential gear (differential) of an automobile, there has been generally known a differential gear in which to accommodate a final drive mechanism including a ring gear, a drive pinion shaft having a pinion gear meshing with the ring gear, and a rolling bearing supporting the drive pinion shaft, and a differential gear mechanism to which the ring gear is bolt-fastened.
In such a differential gear, it is necessary to lubricate the gear and the bearing by lubricant in order to prevent damage or the like to them, and a technique for this purpose is proposed.
For example, in Japanese Patent Application Publication No. 2002-147583 (JP 2002-147583 A) as one example of the related art of the disclosure, a differential housing includes: a differential mechanism chamber in which to accommodate a differential gear mechanism and a ring gear bolt-fastened thereto; and a pinion shaft chamber in which to accommodate a drive pinion shaft and a rolling bearing that supports the drive pinion shaft such that the drive pinion shaft is rotatable. In the differential housing, a feed oil passage for supplying lubricant scooped up by the ring gear to the pinion shaft chamber, and a return oil passage or discharging the lubricant in the pinion shaft chamber to the differential mechanism chamber are provided.
In this case, the lubricant thus scooped up by the ring gear flows into an inlet of the feed oil passage, and then enters the pinion shaft chamber through the feed oil passage. The lubricant thus supplied to the pinion shaft chamber lubricates the rolling bearing, etc., in the pinion shaft chamber, and is then discharged to the differential mechanism chamber through the return oil passage.
Note that, in this related art, the feed oil passage is provided at a position that is offset from the pinion shaft chamber to a ring-gear side in a lateral direction (that is, an axial direction of the ring gear), and the inlet thereof is opened toward a differential-mechanism-chamber side and formed at a position opposed to the ring gear in a radial direction. Accordingly, in this related art, most of the lubricant scooped up by the ring gear enters the pinion shaft chamber, so a sufficient amount of the lubricant can be supplied to the rolling bearing, etc., in the pinion shaft chamber.
In order to bring out and maintain original performance of the rolling bearing and to keep the bearing usable until its calculated life, it is indispensable to lubricate the rolling bearing appropriately. Accordingly, in the related art, the rolling bearing is lubricated by supplying, to the pinion shaft chamber, the lubricant at an amount that immerses the whole rolling bearing in the lubricant.
In the meantime, in the differential, it has been known that, while the device is used, metal abrasion powder (foreign matter) is generated due to repeated meshing and the like between gear wheels, and the foreign matter is mixed in the lubricant. In a state where the rolling bearing is lubricated by the lubricant in which such a foreign matter is mixed, the rolling bearing is damaged earlier than the calculated life of the bearing, starting from a failure occurrence on a bearing raceway surface or the like due to biting of the foreign matter.
In order to improve this problem, it is necessary to prevent the whole bearing from being immersed in the lubricant in which the foreign matter is mixed as much as possible. For this purpose, it is necessary to restrain the supply of the lubricant to the rolling bearing.
However, in the related art, when a rotation speed (the number of rotations) of the ring gear increases, the amount of the lubricant to be scooped up accordingly is increased. As a result, an amount of the lubricant to flow into the feed oil passage becomes larger than that of the lubricant to be discharged from the return oil passage, which frequently causes a poor lubrication state in which the whole rolling bearing is immersed in the lubricant in which the foreign matter is mixed.
On that account, in the related art, a failure of the rolling bearing easily occurs, and it is necessary to improve this problem.